This invention relates to fluxless brazing and more particularly to an apparatus for fluxless brazing in a controlled atmosphere; especially for aluminum workpieces or components such as oil coolers, radiators, heater cores, evaporators, blowers, etc.
The fluxless brazing of aluminum components, such as aluminum radiators and heat exchangers, is normally accomplished by heating the assembly to the brazing temperature while excluding oxygen, thus avoiding oxidation of the parts and preventing incomplete joining. In general, brazing furnaces having a controlled atmosphere or vacuum have been developed for these purposes and, although these methods have been quite adequate for producing brazed parts, proper sealing of a furnace is difficult. The furnaces are generally large, accomodating a number of such component assemblies for batch processing and thus require copious quantities of inert gases or reducing gases to maintain the controlled brazing environment. Should leakage occur and allow the influx of even minor amounts of air, water vapor or other contamination, circulation within the oven exposes the entire batch of parts to contamination and possible loss. Further, where a conveyor furnace is employed for the continuous production of brazed parts, complex door/air locks must be provided for admitting and removing the assemblies while protecting the integrity of the inert atmosphere within the furnace.
Alternative methods have been devised in which the component assembly to be braized is sealed within a box or capsule fitted with an appropriate purging system. The box is then purged to establish the desired environment before being heated by ordinary means such as a furnace or in a fluidized bed heating device to accomplish the brazing. Typical processes employing such capsules are disclosed for example in U.S. Pat. Nos. 3,375,570 and 3,073,268. These prior art processes generally employ seam welding of the box or capsule to accomplish the necessary sealing with the resulting disadvantage that the capsule must be destroyed to obtain the brazed article.
In the U.S. Pat. No. 2,714,760 there is disclosed a method for brazing high temperature alloy parts wherein the brazing step is accomplished by placing the assembly into a retort within a brazing furnace. The retort is fitted with a lid and sealed by means of a sand seal. A reducing gas is supplied to the retort, escaping through the sand seal to maintain the necessary reducing environment. The purging of the retort is accomplished within the furnace, no provision for transfer of the sealed, purged capsule being made.